The present invention relates to a method of controlling engine fuel injection, and is particularly concerned with a method and apparatus for asynchronous injection in an electronic controller of an automobile engine.
An electronic controller of an automobile engine controls the quantity of a gasoline injection in accordance with the air mass which flows into the engine in response to the angle of the accelerator pedal so as to obtain a theoretical air fuel ratio. In other words, it obtains the air mass flow rate of the air flowing into the cylinder, uses an electric circuit such as a microprocessor to obtain a required fuel quantity and then controls the quantity of fuel injection. In the fuel injection control by conventional electronic engine controllers, especially for fuel injection control during acceleration of the automobile, to make up for the shortage of fuel occurring with a synchronous injection during acceleration, an asynchronous injection is performed by using a compensation coefficient obtained by table lookup whose parameter is the throttle opening angle variation, as described on pages 116 to 117 of "Electronic Controlled Gasoline Injection," Sankaido, May 5, 1987.
According to the technique shown in the above-mentioned text, for every engine model a table must be produced by trial-and-error, search of table data with throttle opening angle variations used as one of the parameters. Therefore, such a technique has the disadvantage that a large number of processes are needed for producing the table.
In the first place, the shortage of fuel to be made up for by an asynchronous injection should be specified as a value equivalent to the difference between the air mass flow rate of the air actually drawn into the engine and the air mass flow rate of the air used for calculating the synchronous injection. For this purpose, it is necessary to directly or indirectly use the time of acceleration and the responding air mass flow rate at the inlet port during the early stage of acceleration. However, conventionally no attention has been paid to the time of acceleration in relation to an induction stroke, and the quantity of asynchronous injection has been calculated in most cases by using only an opening angle variation, with the result that excessive or insufficient asynchronous injections still occur with shifts in the time of acceleration. Therefore, prior art attempts have the disadvantage that it is impossible to determine a proper asynchronous injection quantity for achieving a desired air fuel ratio in various drive modes.